fix(2-A3b): complete error-render path, fix link, add supervisor tests

- Add api_key_missing computation to adapters_edit_submit error re-render
  path so the warning and disabled checkbox appear on validation errors
- Fix broken /keys -> /api-keys link in adapters_edit.html template
- Add three supervisor tests:
  - test_start_adapter_refuses_when_required_key_missing
  - test_start_adapter_succeeds_after_key_added_and_clears_last_error
  - test_start_adapter_does_not_check_when_no_requires_api_key
- Add adapters_edit_submit error re-render test:
  - test_adapters_edit_submit_error_rerender_includes_api_key_missing

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/central/gui/routes.py

@@ -1666,6 +1666,17 @@ async def adapters_edit_submit(
             api_key_rows = await conn.fetch("SELECT alias FROM config.api_keys ORDER BY alias")
             api_keys = [{"alias": r["alias"]} for r in api_key_rows]
 
+            # Check if required API key is missing
+            api_key_missing = False
+            requires_api_key_alias = None
+            if adapter_cls and adapter_cls.requires_api_key is not None:
+                requires_api_key_alias = adapter_cls.requires_api_key
+                has_key = await conn.fetchval(
+                    "SELECT 1 FROM config.api_keys WHERE alias = $1",
+                    requires_api_key_alias,
+                )
+                api_key_missing = not has_key
+
             csrf_token = request.state.csrf_token
             response = templates.TemplateResponse(
                 request=request,
@@ -1680,6 +1691,8 @@ async def adapters_edit_submit(
                     "form_data": form_data,
                     "tile_url": tile_url,
                     "tile_attribution": tile_attribution,
+                    "api_key_missing": api_key_missing,
+                    "requires_api_key_alias": requires_api_key_alias,
                 },
                 status_code=200,
             )

src/central/gui/templates/adapters_edit.html

@@ -28,7 +28,7 @@
 {% if api_key_missing %}
 <article aria-label="API Key Required" style="background-color: var(--pico-mark-background-color); margin-bottom: 1rem;">
     <strong>⚠️ API Key Required:</strong> This adapter requires the <code>{{ requires_api_key_alias }}</code> API key to be configured before it can be enabled.
-    <a href="/keys">Configure API Keys</a>
+    <a href="/api-keys">Configure API Keys</a>
 </article>
 {% endif %}